In the manufacture of vaporizable metals, such as magnesium, an effluent is produced by a furnace wherein the metal is being refined. It is important to reclaim as much of the metal as possible in the effluent stack for two reasons. The first is to control potential pollution problems and the second is to reclaim as much of the metal as possible for financial benefit.
In the past, heat pipe designs have been employed which expose a water-filled evaporator to the hot stack gases. As the water vaporizes it is collected at a condenser in normal reflux action. The cooling of the vaporized metal on the exterior wall of the condenser can then be gravity fed from the stack for collection. The utilization of a water-filled heat pipe employing such evaporator and condenser sections is undesirable because the external temperature must be kept below the boiling point of water. Clearly, the attempt to do so in a stack through which a vaporized metal is flowing would present dimensional and control problems.
Suggestions have previously been made to employ a variable conductance heat pipe which modifies the basic evaporator-condenser combination by introducing a charge of non-condensable gas into the condenser which establishes a variably positioned interface within the condenser, depending upon the heat load of the condenser. Such a design is more efficient than the conventional fixed conductance heat pipes but a direct correlation between the volume of the non-condensable gas and the condenser detracts from the compactness of an overall heat pipe unit.